Synthesis and Characterization of a Novel Pentavalent Silane: 1

574

Organometallics 1995, 14, 574-576

Synthesis and Characterization of a Novel Pentavalent Silane: 1-Methyl-1,l-dihydrido-2,3,4,5-tetraphenyll-silacyclopentadiene Silicate, [Ph&4SiMeH2-]*[Kf] Jang-Hwan Hong and Philip Boudjouk" Department of Chemistry, North Dakota State University, Fargo, North Dakota 58105 Received July 26, 1994@ The unambiguous synthesis of the l-tert-butyl-2,3,4,5Summary: The reaction of 1-methyl-2,3,4,5-tetraphenyltetraphenyl-l-silacyclopentadienideanion3avia reduc1-silacyclopentadiene (1) with potassium hydride in THF-ds gives 1-methyl-1,1-dihydrido-2,3,4,5-tetraphe- tive cleavage of the Si-Si bond in bis(1-tert-butylnyl-1-silacyclopentadienesilicate, [Ph&!3iMeH2-l-[Kil 2,3,4,5-tetraphenyl-l-silacyclopentadienyl~ and the com(3), l-methyl-5-potassio-2,3,4,5-tetraphenyl-1-silacyclo-plete NMR characterization of that anion which indi2-pentene (a), and 1-methyl-5-potassio-2,3,4,5-tetraphe- cated substantial n-electron delocalization led us to nyl-1-silacyclo-3-pentene(5). These species are characreinvestigate the reaction of potassium hydride with 1. terized by IH,13C, and 29Si NMR. Treatment of the Careful analysis of the NMR spectrum of the intermedisolution of anions with dimethylchlorosilane gives the ates and characterization of the major product isolated C-substitutedproduct, 1-methyl-2-(dimethylsilyl)-2,3,4,5- from treatment of the intermediates with dimethylchlotetraphenyl-l-silacyclo-3-pentene (2). rosilane clearly show that formation of a silacyclopentadienide anion is not an important pathway for the reaction. In this paper we report that the dominant Introduction pathway in the reaction of potassium hydride with 1 is The interest in silacyclopentadienes2 is largely atsimple addition of the hydride anion to the silicon center tributable to their potential for generating aromatic to give a novel silicate8 absent of highly electronegative silacyclopentadienide anions3 and metallocenes featuratoms on silicon. ing silole i n g ~ Recently, . ~ they have also been used as precursors to silicon containing aromatic d i a n i ~ n s . ~ Results and Discussion Treatment of hydrosilanes with potassium hydride is a known route to silyl anions6 and has been used to When 1 was stirred with KH in DME at -20 "C, a generate silacyclopentadienide anions. Han and Bouddark purple solution was produced that gave, after jouk reported that potassium hydride reacts with l-methtreatment with dimethylchlorosilane, l-methyl-24dimyl-2,3,4,5-tetraphenyl-l-silacyclopentadiene (1) to give ethylsilyl)-2,3,4,5-tetraphenyl-l-silacyclo-3-pentene (2) a species thought to be a silacyclopentadienide anion.7 in 71% yield (eq 1). Corriu et al. later described the reaction of potassium hydride with the less substituted l-methyl-2,5-diphenylPhs m4 1-silacyclopentadiene.6aQuenching of the intermediate anion with DzO gave quantitative yield of the deuterated product, l-deutero-l-methyl-2,5-diphenyl-l-silacyclopentadiene. Abstract published in Advance ACS Abstracts, December 1,1994. (1) This work has been presented in park Hong, J.-H.; Boudjouk, P.; Castellino, S. XXVIth Organosilicon Symposium, Indianapolis, IN, March 26-27, 1993, Abstract, H-3. (2) (a) Dubac, J.; Laporterie, A,; Manuel, G. Chem. Rev. 1990, 90, 215. (b) Colomer, E.; Corriu, R. J. P.; Lheureux, M. Chem. Rev. 1990, 90, 265. (3) (a)Hong, J.-H.; Boudjouk, P. J.Am. Chem. SOC.1993,115,5883. (b) JOO,W.-C.; Hong, J.-H.; Choi, S.-B.; Son, H.-E. J.Organomet. Chem. 1990, 391, 27. (c) Corriu, R. J. P.; Guerin, C.; Kolani, B. Bull. Soc. Chim. Fr. 1985, 973. (d) Hagen, V.; Ruhlmann, K. 2.Chem. 1967, 7, 462. For silafluorenide anions, see: (e) Ishikawa, M.; Tabohashi, T.; Ohashi, H.; Kumada, M.; Iyoda, J. Organometallics 1983, 2, 351. (fl Gilman, H.; Gorsich, R. D. J. Am. Chem. SOC.1968, 80, 3243. (4) Freeman W. P.; Tilley, T. Don.; Rheingold, A. L. J . Am. Chem. soc.1 9 9 4 , m , a 4 2 a . ( 5 ) (a) Hong, J.-H.; Boudjouk, P.;Castellino, S. XXVIth Organosilicon Symposium, Indianapolis, IN, March 26-27, 1993; Abstract, P-50. Hong, J.-H.; Boudjouk, P. Abstracts ofPapers; 206th National Meeting of the American Chemical Society, Chicago, IL, August 22-27, 1993; American Chemical Society: Washington, D.C.; Abstract, INOR 492. Hong, J.-H.; Boudjouk, P.; Castellino, S. XXvTIth Organosilicon Symposium, Troy, NY, March 18-19, 1994;Abstract, P-23. (b) Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics 1994, 13, 3387. ( 6 )(a) Corriu, R. J. P.; GuBrin, C.; Kolani, B. Bull. SOC.Chim. Fr. 1985, 973. (b) Corriu, R. J. P.; Guerin, C. J . Chem. SOC.Chem. Commun. 1980,168.(c) Gilman, M.; Steudel, W. Chem. Ind. 1969, 1094. (7) Han, B.-H.; Boudjouk, P. Chungnam Kwahak Yonguchi 1984, 11,101. Chem. Abstr. 1986,105,6549~. @

(RX = MenSiHCI)

1

2

NMR analysis of 2 led to two noteworthy observations: (1) the dimethylsilyl group exhibits hindered rotation about the bond to the ring carbon, and, (2) only one isomer is produced. Hindered rotation is demonstrated by two methyl doublets of equal intensity with the same coupling constant (J = 3.66 Hz) at 0.21 and 0.33 ppm and a septet of SiH a t 4.49 ppm (J = 3.66 Hz). Irradiation at each doublet collapsed the septet to a quartet with no effect on the other doublet. The claim of a single isomer as the product is based on the observation of only two methyl carbon peaks (-4.63 and -4.71 ppm) for the dimethylsilyl group in the 13C NMR ( 8 )(a)Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. Rev. 1993,93, 1371. (b) Corriu, R. J. P.; Young, J. C. in The Chemistry of Organic Silicon Compounds;Patai, S.,Rappoport, Z., Eds.; John Wiley & Sons: New York, 1989; Chapter 20, pp 1241-1288. (c) Tandura, S. N.; Alekseev, N. V.; Voronkov, M. G. Top. Curr. Chem. 1986,131,99189.

0276-7333/95/2314-0574$09.00/0 1995 American Chemical Society

Notes

Organometallics, Vol. 14, No. 1, 1995 575

spectrum and only one silicon peak (-15.61ppm) for that group in the 29Sispectrum. NMR studies of the purple solution resulting from sonication of 1 and KH for 2 h in THF-ds provide evidence for the intermediacy of three novel anions 3, 4, and 5 in a ratio of approximately 1:0.8:0.8,respectively. lH NMR shows no significant methyl singlet peaks in the SiCH region which should be present if

3

4

J(29Si-1H) = 192-225 Hz in [HZS~(OR)-I'[K+],~J~ and are consistent with a trigonal-bipyramidal structure in which one hydrogen and two carbons of the butadiene moiety occupy an equatorial position. In 13C NMR, three methyl carbons on silicon are observed a t -6.80 ppm for 3,at -0.70 ppm for 4,and a t -5.02 ppm for 5;two carbons of tert-CH at 45.16ppm for 4,43.22ppm for 5;two carbanions of tert-C- at 85.78 ppm for 4 and a t 86.20 ppm for 5. All of these peaks are confirmed by INEPT experiments and are matched to their proton peaks by 13C-lH 2D experiments. Both chemical shifts of the two tert-C- are consistent with the observations of O'Brien, in which chemical shifts of the carbanions of l,l-dimethyl-2,3,4,5-tetraphenyl-lsilacyclopentadiene are observed from 75.3to 89.4ppm (eq 3).12

5

the SiH proton in 1 were removed by the hydride. Instead, the major absorptions attributable to SiCH were a triplet a t 0.16ppm and two smaller doublets a t -0.23 and 0.34ppm. In addition to these SiCH peaks, three SiH absorptions and two tert-CH absorptions were observed with phenyl and solvent peaks. The SiH absorptions consisted of a pair of overlapped quartets at 3.79 ppm, a quartet a t 4.26 ppm, and a doublet of quartets at 5.19ppm. The two tert-CH absorptions are composed of a singlet at 3.03 ppm and doublet a t 3.30 ppm. The three groups of absorptions (SiCH, SiH, and tert-CH) are complex but all coupling relationships of SiCH, SiH, and tert-CH can be definitively assigned using homo decoupling experiments. Irradiation a t 3.79 ppm (overlapped quartets of SiH) collapsed the triplet of SiCH a t 0.16 ppm to a singlet (3);irradiation at 4.26 ppm (quartet of SiH) collapsed the doublet of SiCH a t 0.34 ppm to a singlet (4). Irradiation at 5.19 ppm (doublet of quartets of SiH) collapsed the doublet of SiCH at -0.23 ppm and the doublet of tert-CH at 3.30ppm to singlets, respectively (5). Irradiation a t 3.30 ppm (doublet of tert-CH) collapsed the doublet of quartets of SiH a t 5.19 ppm to a quartet (5). The positions of the hydrogens on silicon in 3 are distinguishable: overlapped quartets of SiH (3) a t 3.79ppm rather than a simple quartet indicates the presence of one axial hydrogen and one equatorial hydrogen on silicon. However, the nearly identical chemical shifts of these hydrogens voided a decoupling experiment: irradiation a t 0.16 ppm (the triplet of SiCH) collapsed SiH absorptions to a broad singlet rather than the anticipated pair of separated singlets. As expected, 2J (lH-lH) coupling was not observed because axial-equatorial coupling constants are typically very small.g The coupled 29Si{1H} spectrum resolved the three silicon resonances of the decoupled 29Sispectrum into a doublet of doublets at -36.30 ppm (J8i-H = 192.5 and 179.6Hz) (3),a doublet at 7.92ppm (JSi-H = 177.8Hz) (41,and a doublet at -3.29 ppm (JSi-H = 168.7Hz) (5).1° The Si-H coupling constants in 3 are also very close to (9) Corriu, P.; GuBrin, C.; Henner, B.; Wang, Q.Organometallics 1991,10, 3574. (10)For a discussion of the effects on chemical shift of forming a pentacoordinatebond to silicon, see: Williams E. A. In The Chemistry of Organic Silicon Compounds; Patai, S.; Rappoport, Z., Eds.;New York, Wiley, 1989; pp 537-540.

Ca 77.4 ppm 75.3 ppm 89.4 ppm CP The carbanions in 4 and 5 polarize the attached phenyl groups. The chemical shifts of C, and Cmin the two phenyl groups are shifted upfield, the chemical shifts of C, are farther upfield than those of Cm: 110.75 ppm for C, and 114.93ppm for C m of the phenyl bonded to tert-C- of 4 and 111.38 ppm for C, and 115.38 ppm for Cm of the phenyl bonded to tert-C- of 5. Similar polarization of phenyl groups has been observed in other 5b Moreover, all 16 tert-C peaks (4from silole ani~ns.~*l 3 due to its mirror plane, 6 from 4,and 6 from 5) are observed and confirmed by INEPT experiments. Of the possible 26 peaks in the aromatic CH region (C,,, Cm, and C,: originally 26 peaks in 123-131 ppm, 6 from 3 due to its mirror plane, 10 from 4,and 10 from 5),18 were observed and could be assigned. Presumably, accidental overlap of some peaks is responsible for the reduced number of peaks. In 'H NMR we observed that the smaller pairs of doublets for 4 and 5 increased with time. Simultaneously, we also observed that 3 diminished to a final ratio of approximately 1:1.4:1.4for 3:4:5,respectively. No evidence that 3 is the source of 4 and/or 5 or that an equilibrium is operating was obtained. We also determined that the singlet peak attributed to a methyl on silicon in the l-methy1-2,3,4,5-tetraphenylsilacyclopentadienide anion in an earlier report7 is actually the methyl peak on polymethylsiloxane which forms when water is present in the reaction mixture. Base cleavage of both Si-C bonds in silole rings has been reported.13 Conclusions Potassium hydride undergoes an addition reaction tetraphenyl-1-silacyclopentadiene with 1-methylS,3,4,5(11) Corriu, R. J. P.; GuBrin, C.; Henner, B.; Wang, Q.Organometallics 1991, 10, 2297. Breeden, D. J . Am. Chem. SOC.1981,103,3237. (12) O'Brien, D.H.; (13) (a) Atwell, W. H.; Weyenberg, D. R.; Gilman, H. J. Org.Chem. 1976,32, 885. (b) Balasubramanian, R.; Gerge, M. V. J. Organomet. Chem. 1975,85,311. (c) Curtis, M.J . Am. Chem. Soc. 1969,91,6011.

576 Organometallics, Vol. 14, No. 1, 1995 Table 1. 'H, 'H 13c

29Si

SiMe SiH CH SiMe CH Cc, of cc, of cSiof ring

Notes 13C, and

29SiChemical Shifts of 1 and 3-5

10

3b

46

Sb

0.57 (d, 3H, J = 4.15) 5.00 (q, IH, J = 4.15) none -6.94 none none none none -11.81

0.16 (t, 3H, J = 4.40) 3.79 (overlapped q, 2H) none -6.80 none none none none -36.30(dd, J s ~ H ~192.5, = J s s e = 179.6)

0.34 (d, 3H, J = 3.66) 4.26 (q, lH, J = 3.66) 3.03 (s, 1H) -0.70 45.16 85.78 110.75 114.93 7.92 (d, J s i = ~ 177.8)

-0.23 (d, 3H, J = 3.66) 5.19 (q of d, 1H) 3.30 (d, lH, J = 4.40) -5.02 43.22 86.20 111.38 115.80 -3.28 (d, Jsi~= 168.7)

a In CDC13, reference; CDCl3 = 7.27 ppm for 'H-NMR, CDC13 = 77.00 ppm for I3C-NMR, extemal Me& = 0.00 ppm for 29Si-NMR. In THF-ds, reference; THF-ds = 1.73 ppm for 'H-NMR, THF-ds = 25.30 ppm for I3C-NMR, external Me& = 0.00 ppm for 29Si-NMR.

a greenish yellow solution. After removing solvent and MezSiHC1under reduced pressure, the residual solid was extracted with hexane. Several recrystallizations in hexane gave 2 as colorless crystals (yields: 71% in DME at -20 "C, 43% in THF -20 "C, 30% in THF at room temperature),mp, 132-133 "C; 'H and NMR patterns of 2 in CDCl3 are not different from in benzene-&. 'H-NMR (CDCb, ref solvent = 7.27ppm), 0.21 (d, 3H, SiMez, 3Jpde-~ = 3.66 Hz), 0.33 (d, 3H, SiMez, %JM~-H = 3.66 Hz), 0.60(d, 3H, SiMe, %JM~-H = 3.66 Hz), 3.86 (d, l H , CH, 3 J ~=- 4.40 ~ Hz), 4.03 (quint, lH, SiH), 4.49 (sept, lH, SiH, 3 J ~ e=-3.66 ~ Hz), 6.9-7.8(brd m, 20 H, Ph). W-NMR (CDC13,ref: solvent = 77.00ppm), -4.26 (SiMe), -4.63,-4.71 (SiMez), 39.85 (tert-CHI, 43.33 (CSiMeZH), 124.22, 124.28, 125.91,126.65 (para carbons of four phenyl groups), 127.21, 127.34,127.90,128.11,128.42,129.01,130.17,130.96(ortho and meta carbons of four phenyl groups), 139.92, 141.48, 142.32,143.49,144.81,146.76((23,C d , and ipso carbons of four Experimental Section phenyl groups). 29Si-NMR(CDC13,ref: ext TMS), -15.61 (HSiMez), 28.45 (HSiMe). MS (M+,relative abundance) m l z General Procedures. All reactions were performed under 461 (M+ 1, 5), 460 (M+, 131,400 (M+ - 60,loo), 197 (481, an inert nitrogen atmosphere using standard Schlenk tech121 (74),59(50).Anal. Calcd for C~H32Siz:C, 80.81;H, 7.00, niques. Air-sensitive reagents were transferred in a nitrogenFound: C, 81.13;H, 6.94. filled glovebox. THF and DME were distilled from sodium NMR Study of the Reaction of l-Methyl-2,3,4,S-tetbenzophenone ketyl under nitrogen. Hexane was stirred over raphenyl-l-silacyclopentadiene(1) with KH. l-Methylconcentrated HzS04 and distilled from CaH2. NMR spectra 2,3,4,5-tetraphenyl-l-silacyclopentadiene(1) (0.141g, 0.351 were recorded on JEOL GSX270 and GSX400 spectrometers. mmol) and KH (0.018g, 0.45mmol, 1.27equiv) were placed GC-MS and solid sample MS data were obtained on a Hewlettin a 5-mm NMR tube followed by THF-ds (1.5mL). Sonication Packard 5988A GC-MS system equipped with a methyl silicon of the NMR tube for 2 h changed the color of the solution from capillary column. Elemental analyses were done by Desert yellow to red and finally t o a deep violet. NMR studies were Analytics (Tucson, AZ). l-Methyl-2-(dimethylsilyl)-2,3,4,5-tetraphenyl-l-silac~ carried out on samples prepared in this fashion. 'H, 'H-IH clo-3-pentene(2). 1-Methyl-2,3,4,5-tetraphenyl-l-silacyclo- homo decoupled, I3C, INEPT I3C, 'H-I3C coupled 2D, 29SiNMR, and 29Si-protoncoupled NMR data were obtained and pentadiene (1)16(2.50g, 5.50 "01) and KH (0.27g, 6.73mmol, NMR data not included in Table 1: are listed in Table 1. 1.22 equiv) were placed in a 100 mL flask with 60 mL DME. 158.21,157.44,150.96,149.37, 148.88,148.80,147.05,146.99, After stirring at -20 "C for 40 min, the greenish yellow slurry 146.02,145.80,130.51,128.85,128.05,126.95,111.53,111.38 turned bright red and finally dark purple. Stirring was (tert-C),131.05,128.78,128.51,128.33,128.17,127.75,127.59, continued for 8 h at -20 "C. Filtration of the mixture under 127.30,127.25,126.69,125.53, 125.16,124.74,124.26,123.07, nitrogen produced a deep violet solution. This solution was 122.99,115.57,114.75(aromatic CH). added to an excess of MezSiHCl(1.20mL, 11.0mmol) in DME at room temperature. Stirring for an additional 3 h produced

(1) to form the pentavalent anion, l-methyl-1,l-dihydrido-2,3,4,5-tetraphenyl-l-silacyclopentadiene silicate, [Ph&&iMeHz-l.[K+] (31, unique in its composition because of the absence of electronegative atoms on silicon, and two isomeric anions in which the negative charge is on carbon. NMR studies were able to distinguish the axial and equatorial hydrogens in 3. These results provide strong evidence in support of Corriu's postulation that hypervalent silicon dihydrides are formed in the racemization of l-NpPhMeSi*H14and of Ishikawa's proposal that silyllithium and organolithium reagents may add t o siloles and silafluorenes to give ~i1icates.l~ This study also corrects the earlier report7 that potassium hydride abstracts a proton from 1.

+

(14)Brefort, J. L.;Corriu, R.; GuBrin; Henner, B. J. Organomet. Chem. 1989,370,9. (15)(a) Ishikawa, M.; Tabohashi, T.; Sugisawa, H.; Nishimura, K.; Kumada, M. J. Orgunomet. Chem. 1983,250,109.(b) Ishikawa, M.; Tabohashi, T.; Ohashi, H.; Kumada, M.; Iyoda, J. Organometallics 1983,2,351. (c) Ishikawa, M.;Nishimura, K.; Sugisawa, H.; Kumada, M. J. Orpanomet. Chem. 1981.218.C21. (16)B&djouk, P.; Sooriyakuma;an,R.; Han,B.-H. J. Org. Chem. 1988,51,2818.

Acknowledgment. Financial support from the Air Force Office of Scientific Research through Grants 910197 and F49620-92-5-0431,the National Science Foundation through Grant No. EHR-9108770, and the Korea Science and Engineering Foundation (J.-H.H) is gratefully acknowledged. OM9405910